Inspection of hidden structure

ABSTRACT

An inspection apparatus determines information indicative of structure that may be hidden behind an obscuring boundary, such as a wall. A processor collects measurements of properties characterizing the hidden structure and measurements of location of the apparatus. The collected data are mapped to produce an image of intensity in the characteristic measurements. Each intensity value in the image reflects a measure of density, of material type, or of some other specific information by which hidden structure can be discerned. The intensity changes indicating the hidden structure are displayed to a user via color-coded pixels or the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of patent application Ser. No.13/081,476, filed Apr. 6, 2011, which claims benefit of priority ofprovisional patent application 61/321,322, filed on Apr. 6, 2010, thedisclosure of which is incorporated herein by reference.

BACKGROUND

The present general inventive concept is directed to moving spatialsensors and associated image and signal processing for inspection ofmaterials and/or structure in a region of interest. The generalinventive concept finds applicability in, among other things, imaging ofhidden structures and objects in and behind obscuring surfaces, such as,for example, walls. The present general inventive concept achievesbenefits over other devices, such as so-called “stud-finders” and otherrelated construction and building inspection tools, by providing aspatial image of the area hidden by an obscuring barrier, such as wallcovering material.

Conventional stud finders provide users with information relating tohidden structure in walls, such as the positions of wooden and metalstuds, and in some cases, electrical wires or pipes. This is achieved byan assortment of data acquisition techniques, including measurements ofmaterial density or material transitions via, among others, RF,ultrasonic, magnetic, electrical and dielectric capacitancemeasurements. Stud finders are typically divided into those that detectthe center of the stud, or other object of density, and those thatdetect edges at a sharp density transitions. One limitation in theprevailing art is that only a single stud, or other object of interest,can be visually located at one time, using the hand-held devices'built-in indicators. Typical designs allow only a small region to beexamined at a time; it is up to the user to mark the wall in such a wayas to make sense of the overall structure behind it. If exploring thewall to seek out specific structures, as opposed to just the neareststud, extensive marks with tape, pen, pencil or the like must be madebefore the hidden structure can be visualized. An additional limitationis that the sensors are generally preferentially biased to detecttransitions in only one dimension. While this is adequate for theprimary task of stud finding, it requires the user to rotate the deviceand start over to look for other structure, such as horizontal blockingbetween studs. In the case of ceilings, floors, or other arrangements inwhich structural members are concealed, a user may be required topossess and apply learned experience in determining the expectedorientation of studs, beams, joists, etc. A further limitation ofpresent devices is in dynamic range; conventional devices are generallyself-calibrating and require learned finesse on the part of the user andoften multiple attempts in order to successfully identify internal wallstructure. Moreover, devices of present art generally reduce sensitivityto accommodate the strongest sensor return, thus making it verydifficult to detect multiple hidden objects of differing densitiesand/or depths without many small iterative passes across the wallsurface.

SUMMARY

The present general inventive concept provides a coupling of a sensor bywhich hidden structure can be detected, such as a density sensor, to asystem for tracking position in one, two, or three dimensions. Theinformation obtained from such coupling may be accumulated from multiplesensing points and imaged onto a display system to present atwo-dimensional depiction of structure obscured by a boundary. Incontradistinction with conventional devices, the image produced byembodiments of the present general inventive concept, thetwo-dimensional image presented to the user spatially corresponds to theregion traversed in multiple directions by the sensors.

The foregoing and other utility and advantages of the present generalinventive concept may be achieved by an apparatus to inspect a region ofinterest for structure therein. A sensor generates at least onecharacteristic signal responsive to at least one structuralcharacteristic of the region of interest at a location on a surfacetherein of the sensor. The same or another sensor generates a positionsignal indicative of the location on the surface. A processor generatesnumerical values from the characteristic signal and the position signalas the sensor is translated over the surface and establishes anassociation between the numerical values generated from the positionsignal and the numerical values generated from the characteristicsignal. A display generates a two-dimensional image from the associatednumerical values so as to be perceived by a human user. The displayedimage represents the structure in the region of interest obscured by andparallel to the surface.

The foregoing and other utility and advantages of the present generalinventive concept may also be achieved by an apparatus to inspect aregion of interest. The apparatus includes an inspection sensor having apredetermined contact area over which a characteristic measurement ismade thereby at a location on a surface in the region of interest. Aposition/motion sensor determines the location at which thecharacteristic measurement is made. A data storage unit stores a datamap in which map values are stored in correspondence with apredetermined coordinate system. A processor collects successivecharacteristic measurements from the inspection sensor made along a scantrajectory. Numerical values are generated from the characteristicmeasurements and the map values are computed from the numerical values.The processor stores the map values in the data map such that locationsin the scan trajectory at which respective characteristic measurementsare made spatially correspond with the coordinate system of the datamap. A two-dimensional image of pixels is displayed on a display, wherethe pixels are assigned pixel values determined from the map values. Theimage is centered in a graphical window positioned in the display inaccordance with the locations in the scan trajectory.

The foregoing and other utility and advantages of the present generalinventive concept may also be achieved by a method of determiningstructure obscured by a surface in a region of interest. A data map isestablished that is indexed in accordance with a predeterminedcoordinate system. Characteristic measurements are obtained bytranslation of a sensor over the surface, where the characteristicmeasurements are made at arbitrary locations along a scan trajectorythrough which the sensor is translated. Numerical values of thecharacteristic measurements are mapped to numerical values indexed inthe data map. A two-dimensional image of pixels is displayed, where thepixels are arranged per the predetermined coordinate system and areassigned pixel values corresponding to the numerical values indexed inthe data map.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and utilities of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of exemplary embodiments, taken in conjunctionwith the accompanying drawings, of which:

FIG. 1 is conceptual block diagram illustrating basic functionality ofembodiments of the present general inventive concept;

FIG. 2A is a schematic block diagram of a minimal sensor arrangement bywhich the present general inventive concept may be embodied;

FIG. 2B is a conceptual block diagram of an exemplary data acquisitionand mapping process usable with embodiments of the present generalinventive concept;

FIG. 3 is a flow diagram of an exemplary data acquisition and displayprocess by which the present general inventive concept may be embodied;

FIG. 4 is an illustration of an exemplary application of an embodimentof the present general inventive concept;

FIGS. 5A-5C are illustrations of a hand-held embodiment of the presentgeneral inventive concept;

FIGS. 6A-6B are schematic block diagrams of exemplary systemconfigurations by which the present general inventive concept may beembodied;

FIGS. 7A-7B are illustrations of exemplary characteristics sensorarrangements usable in certain embodiments of the present generalinventive concept;

FIG. 8 is an illustration of an inspection apparatus embodying thepresent general inventive concept implementing an optional markingfeature;

FIGS. 9A-9C are illustrations of embodiments of the present generalinventive concept utilizing separable system components;

FIG. 10 is an illustration of an inspection apparatus embodying thepresent general inventive concept implementing an image projectingdevice; and

FIG. 11 is an illustration of an inspection apparatus embodying thepresent general inventive concept implementing an alternative imageprojecting device.

DETAILED DESCRIPTION

The present inventive concept is best described through certainembodiments thereof, which are described in detail herein with referenceto the accompanying drawings, wherein like reference numerals refer tolike features throughout. It is to be understood that the terminvention, when used herein, is intended to connote the inventiveconcept underlying the embodiments described below and not merely theembodiments themselves. It is to be understood further that the generalinventive concept is not limited to the illustrative embodimentsdescribed below and the following descriptions should be read in suchlight.

Referring to FIG. 1, there is illustrated an exemplary inspectionapparatus 100 by which the present invention may be embodied. Theinspection apparatus 100 is compartmentalized into exemplary subsystemsfor purposes of explanation: a sensor subsystem 120 to generate signalsindicative of a position in a region of interest and a characteristicvalue at the position, a processing subsystem 140 to process the signalsinto a map of hidden structure in the region of interest, a graphicssubsystem 150 to graphically display the map in a meaningful way to auser, and a communications subsystem 130 to coordinate and convey dataand control signals between subsystems. It is to be understood that thedistribution of functionality across the exemplary subsystemsillustrated in FIG. 1 is for purposes of description and not limitation;numerous alternative system configurations can be used to embody thepresent invention without deviating from the spirit and intended scopethereof.

The sensor subsystem 120 may be placed proximal to or in contact with asurface 115 of an inspection region 105, which, as used herein, refersto a region in space in which direct inspection of objects of interestis prevented. As illustrated in FIG. 1, inspection region 105 includessurface 115, which obscures and prevents direct inspection of structure117. Structure 117 may be present in the inspection region 105 fornumerous of reasons, such as, for example, due to man-made or naturalconstruction in the inspection region 105 or as unintended byproducts ofman-made or natural processes. Such structure 117 may be detected bysuitable probing techniques that sense variations in physical propertiesin inspection region 105, representatively illustrated as changes inmaterials 110, 112. Data acquisition by which such variations inphysical properties are obtained is referred to herein as acharacteristic measurement.

In accordance with achievable benefits of the present invention, sensorsubsystem 120 may be moved within inspection region 105, such as in theX/Y plane defined by surface 115, to obtain characteristic measurementsof hidden structure 117. It is to be understood that although surface115 is illustrated in FIG. 1 as a planar surface, the present inventionis not limited thereto. For example, when implemented with suitablesensors, sensor subsystem 120 may characterize hidden structure 117obscured by a barrier that is spatially variable in three dimensions.Sensor subsystem 120 generates signals by which structural variabilityin inspection region 105 may be discerned despite the obscuring barrier.For example, sensor subsystem 120 may include one or more devices thatcan produce at least one signal from which characteristics of hiddenstructure may be ascertained, including, but not limited to sensors thatdetect changes in capacitance, refractive index, magnetic fields orelectric current, radio-frequency signal echo returns, ultrasonic echoreturns, edge-finders, center-finders, A/C or D/C voltage detectors,thermal and optical detectors, and other sensing devices suitable fordiscerning material density or type, shapes or edge features. Sensorsubsystem 120 may also include one or more devices that can produce atleast one signal indicative of position, or change in position,including, but not limited to accelerometers, rotational encoderscoupled to one or more balls or cylinders, and optical motion detectors.Additional means for sensing location can be employed, including devicesthe determine distance from a base point, such as may be measured byradio frequency (RF) or ultrasonic time of flight and geo-positioning,such used by the Global Positioning System (GPS). In certain embodimentsof the present invention that track a change in position of sensorsubsystem 120, as opposed to in indication of absolute position, anorigin may be established against which relative location can betracked.

The characteristic and position signals may be converted into numericalvalues, such as by a suitable analog-to-digital (A/D) device, and acharacteristic measurement value may be associated with one or moreposition values corresponding to the spatial position at which thecharacteristic measurement value was obtained. Exemplary processingsubsystem 140 maps the associated numerical values to a data map,renders an image of image pixels corresponding to the mapped data, anddisplays the image on a display 152 of graphics subsystem 150. Thus, inaccordance with achievable benefits of the present invention, hiddenstructure 117 is faithfully represented to a user through atwo-dimensional image on display 152.

Exemplary communication subsystem 130 transfers various signals betweensubsystems of inspection apparatus 100 through a set of communicationlinks 132, 134, 136, which may be implemented in a suitable medium forcarrying signals between components. For example, any of communicationlinks 132, 134, 136 may be implemented in electrical conductors,including wires, cables, printed circuits, optical media, such asoptical fibers, air, vacuum, etc. Moreover, the communication links 132,134, 136 need not be implemented in the same medium, whereby multiplesystem component groupings can be realized. For example, certainsubsystem components may be contained in the same housing separate fromother subsystem components. Accordingly, the system components sharing ahousing may communicate in one medium, e.g., printed circuit wiring, andmay communicate with other system components via another medium, e.g., awireless communication link. The ordinarily skilled artisan willrecognize and appreciate that a variety of physical groupings of systemcomponents that may be achieved by prudent selection of communicationmedia, housings, casings, chasses, etc. The present inventionintentionally embraces such alternative embodiments.

FIG. 2A depicts an exemplary sensor arrangement 200 in sensor subsystem120 by which data acquisition may be achieved in accordance with thepresent invention. Sensor arrangement 200 includes an inspection sensor210, by which a characteristic measurement may be obtained, and aposition/motion sensor 220, by which a location on surface 205 isobtained. The sensors 210, 223 may be coupled to a processor 240, bywhich electrical signals therefrom may be conditioned, sampled,converted to numeric values and assembled into data structures inaccordance with the present invention. As illustrated in figure, sensors210, 220 may be separated by a known distance D, which may becompensated for in determining the actual location of the characteristicmeasurement by inspection sensor 210. Further, it is to be observed thatinspection sensor 210 may have a contact area on surface 205,representatively illustrated by dimension W_(I), which is greater thanthat of the position/motion sensor 220, which is representativelyillustrated as dimension W_(P). It is to be understood that while theterm contact area is used for purposes of description, one or moresensors 210, 220 may not physically come in contact with surface 205.Contact area, as used herein, refers to an area on surface 205 overwhich any one characteristic measurement and/or position determinationis made, regardless of whether actual contact with the surface is made.Thus, an effective contact area may include areas that are larger orsmaller than the actual surface area of a sensor, which may, in turn,affect the depth of the sensing field into the material.

In FIG. 2B, there is illustrated a conceptual block diagram of anexemplary data acquisition and processing technique as may beimplemented in embodiments of the present invention. Each circularregion, representatively illustrated at circular region 255, representsa contact area of inspection sensor 210 having a diameter W_(I). It isto be understood that although contact areas 255 are illustrated asbeing circular, contact areas of various shapes may be used inconjunction with the present invention without departing from the spiritand overall scope thereof. Additionally, the dimension R_(P) in FIG. 2Brepresents the finest resolution in position detectable byposition/motion sensor 220. It is to be understood that the dimensionR_(P) is illustrated in FIG. 2B as being substantially equivalent in theX and Y directions, such is solely for convenient illustration purposesand is not intended to limit the present invention. It is to beunderstood further that the actual distance between measurements varyacross embodiments, but will generally depend on the translation speedof sensors 210, 220, the trajectory 260 of the translation and thesampling rate of processor 240, among other things.

The ordinarily skilled artisan will appreciate that certain sensors thatmay be used in embodiments of the present invention are not uniformlyresponsive across the sensing area. As such, the same structure in aregion of interest may produce a larger or smaller signal depending uponthe placement of the sensor relative thereto. Certain characteristicmeasurement sensors, such as density sensors, may produce the strongestsignal responsive to structure that is centered on the contact area andproduce increasingly weaker signals when such structure is locatedfurther away from centered on the contact area. In contrast, othermeasurement sensors, such as edge-detecting sensors, may produce thestrongest signal when a material transition in the hidden structure,such as an edge, is centered in the contact area and oriented in apreferred direction for the sensor design. Additionally, certain sensorswill respond differently depending upon the depth into the material thatthe sensing field can penetrate. The proportional response of aparticular sensor to the location and orientation of structure in theregion of interest relative to the contact area is referred to herein asthe sensor's spatial sampling function.

In certain embodiments of the present invention, the data that areultimately processed and displayed are arranged in a predetermined maparrangement 250, such as on a rectangular grid illustrated in FIG. 2B,of spatial resolution defined by dimension R_(X) and R_(Y). At eachlocation 252 in data map 250, a numerical value is stored that iscomputed from one or more measurements as sensors 210, 220 aretranslated across the surface 205. It is to be understood that otherdata arrangements can be used with the present invention withoutdeparting from the spirit and overall scope thereof. However, it will beappreciated by the skilled artisan that representation of measurementvalues in a rectangular grid lends naturally to display of thisinformation on pixel-based graphics subsystems.

Characteristic measurements may be made along a scan trajectory 260 at alocation on surface 205 denoted by (i, j). As used herein, a scantrajectory refers to directed motion in one, two or three dimensions inthe region of interest over which characteristic measurements are madeat arbitrary locations thereon. It is to be understood that whiletrajectory 260 is illustrated in FIG. 2B as proceeding from left toright, a typical scan trajectory will be made in left to right, up todown, down to up, right to left, circular, diagonal, etc., directions tocover a desired area. A scan trajectory may, in certain embodiments ofthe present invention, proceed according to directed raster scan.However, in certain embodiments of the present invention, such as inhand-held devices, a scan trajectory 260 may be any free-form path onsurface 205.

As motion over surface 205 proceeds, processor 240 will obtain a k-thcharacteristic measurement F_(k)(i, j). As is illustrated in FIG. 2B,overlap of sensed regions may exist, representatively illustrated atoverlap 257, between the contact area over which F_(k)(i, j) is made andthe contact area of previous measurements. Given that the sensor isresponsive in accordance with a spatial sampling function,F _(k)(i,j)=[d(x,y,z)

S]|_((x,y)=(i,j)).

Thus, F_(k)(i, j) may be considered as the convolution of the actualcharacteristic, e.g., density d(x, y, z) measured at the surface withthe spatial sampling function S inherent to the sensor evaluated at (x,y)=(i, j). The practical effect of this is that one measurement F_(k)taken at sample time k represents the sensor's weighted estimation ofthe structural characteristic, e.g., density, measured at the surface ofthe region of interest from the volume that is under the sensor'scontact area.

In accordance with embodiments of the present invention, themeasurements F_(k)(i, j) are mapped at locations (x, y) thereinaccording to M: {F₁, . . . , F_(k)}→φ(x, y), where φ(x, y) is anestimate of d(x, y), the actual density of the material at for point (x,y) in map 250. That is, each data location 252 in map 250 may becomputed from any and all measurements made over one or more contactareas corresponding in position to the coordinate (x, y) therein.Moreover, in certain embodiments of the present invention, map 250 iscontinuously updated as sensors 210, 220 proceeds along trajectory 260.

To illustrate an exemplary operation M, it is to be assumed that asensor has an inherent spatial sampling function that shapes theresponse thereof to the density of material under the contact area inaccordance with an isotropic Gaussian, i.e., centered at the middle ofthe contact region and falling off with standard deviation of σ. Suchoperation M maps the characteristic measurement data to a fixed gridwith spacing of, say, R_(P), the minimum spatial resolution of positionsensor. If σ is small in relation R_(P), then each characteristicmeasurement F_(k) can simply be mapped to the nearest data location 252in the map 250. The operation M is in this case uncomplicated, sincethere is little spatial spread of the sampling function. However, if asensor is used with a large σ in the sampling function, then, tomaintain spatial accuracy of the estimates, overlap of the samplingfunctions for neighboring characteristic measurements cannot be ignored.It will be understood and appreciated by those skilled in the art thatthe characteristic measurements may be treated as a decomposition of theactual physical density function d(x, y).

That is, d(x, y)≈Φ(x, y)=ΣF_(k) φ(x_(k), y_(k)), where φ(x_(k), y_(k))is a locally supported weighting function that spans an area around thesampled point (x_(k), y_(k)). The sum is taken over all samples k forwhich the characteristic measurements F_(k) are taken over contact areasthat significantly overlap the map point 252 for (x, y).

When spatial sampling functions are substantially orthogonal, thespatial sampling functions, normalized to unit area under itscharacteristic curve, may be applied directly as decomposition basiselements φ. The characteristic measurement F_(k) may then be distributedto all points in the grid neighborhood around (x_(k), y_(k))proportionally weighted by the sample function so that the total of theincrease of the local data values sums to F_(k). Where the spatialsampling functions significantly overlap and are not orthogonal,additional measures must be taken to avoid counting characteristicmeasurement information twice. One means of achieving an accuratelocalized density estimate is to begin with the measurement F_(k)centered on the point of interest (x_(k), y_(k)) and to subtractmeasurements taken in the neighborhood around this point in proportionto the overlap of the neighboring sampling functions. As will beunderstood by those skilled in the art, this overlap may be calculatedfrom the inner products of each normalized sampling function with itsneighbor, in a process consistent with, for example, the Graham-Schmidtprocess. In certain specific cases, which will be understood by thoseskilled in the art, non-orthogonal overlapping sampling functions mayform a mathematical frame that behaves in manner similar to a basis,i.e., such that the summed sampling functions have constrained totalarea under the curve and treated as if no overlap existed.

In certain embodiments of the present invention, contact area overlapmay be treated as viewing each measurement F_(k) as a sample of anunknown underlying density distribution, and to estimate, using jointinformation from all overlapping samples, the maximum likelihooddistribution of actual materials behind obscuring surface. Bayesian andother statistical analyses may be used to achieve such an estimate froma set of characteristic measurements. The joint information may bereduced to a single density surface estimate using orthogonal matchingpursuits or simultaneous orthogonal matching pursuits, as will beunderstood by ordinarily skilled artisans. Other equivalent techniquesfor mapping arbitrarily located measurements onto a fixed grid includesparse approximation and compressive sensing, which may be used inconjunction with the present invention without departing from the spiritand intended scope thereof.

In certain embodiments of the present invention, each characteristicmeasurement sample F_(k) may be stored in a storage device.Alternatively, only values 252 in the map 250 are stored andprogressively updated, and individual measurements F_(k) are discardedfrom memory once mapped onto the data map 250. Storing the history ofmeasurements has the advantage that at each point, joint informationfrom all samples may be reconsidered to produce a best approximate map.On the other hand, storing only the working data map 250 simplifiescomputational and memory requirements.

Embodiments of the present invention can progressively improve datadetail in the data map 250 and images derived therefrom as follows. Afirst characteristic measurement F_(k) may be made and data map 250 maybe populated by adding values to locations 252 around the correspondingpoint (x, y) as weighted by the sampling function of the sensor. Thesensor subsystem 120 is moved and a second measurement is made, etc. Forthis and each subsequent measurement, data map 250 is updated byexamining jointly the existing density values in map 250 and thelocation and sampling function applicable to the new measurement andadjusting the density of displayed pixels in the neighborhood around thenew measurement point to the least extent that is still consistent withthe new measurement. For example, by summing the new measurementresponse with the previously populated data map 250, and thenreweighting the data values in a surrounding neighborhood as the newmeasurements are taken, an iteratively improving density map 250 may beproduced as measurement values corresponding to partially overlappingcontact areas accumulate in the vicinity of each location 252.

In certain embodiments of the present invention, sensors are employedthat detect edges in a preferred orientation. For example, a spatialsampling function may provide maximal response when an edge is orientedperpendicular to the sensor and falls in its center, and falls off withdistance squared only in the direction perpendicular to the edge. To mapsensor data to a fixed grid with spacing R_(p), for example, it is firstto be noted that in order to sense edges in both X and Y directions, atleast two orthogonal sensors are required, such as is illustrated inFIG. 7B. Sensors 763, 767 are orthogonal and spatially displaced. Thus,each measurement F_(k) will have two disjoint components as a sensorcontact area, and each component of the contact area will have aresponse function that corresponds to detection of an edge in itscenter. If, for example, sensor 767 detects vertical edges and sensor763 detects horizontal edges, edges that are at an angle will bepartially detected by both sensors. In order to capture informationabout edges in both orientations at each point (i, j) over the obscuringsurface, the sensor configuration 750 must be moved in a way that bothsensor regions eventually pass over each point of interest on thesurface. The operation M to map measurements to data map 250, andaccordingly to a display, may have several processing components.Respective responses of each sensor 767, 763 may be examined for extremato locate edges at location (i, j) in each sensor's particularorientation. Two separate maps 250 containing edge-like feature data maythus be generated. The separate maps may then be registered one with theother and a joint edge-response may be calculated for each point in theresulting data map 250. Such process may produce an edge plot and, withsufficient sampling, the embodiment may display a suitably coded pixelfor each point at which an edge is detected, thus depicting, forexample, studs and pipes by their edge outlines in the display. Inanother embodiment, a joint estimate of the orientation of an edge maybe determined by, for example, evaluating the X edge data and Y edgedata as respective derivatives in the X and Y directions and forming agradient vector from their combined readings at each point (x_(k),y_(k)). The resulting data may be displayed through oriented bars ofpixels that correspond in length to the width of the contact area. Whenso embodied, the appearance of solid estimated edges is provided evenwhen the scan trajectory has not densely covered the surface.

In certain embodiments of the present invention, domain knowledge oflikely features may be applied to improve the informational content ofthe displayed data. For example, the dimensions and orientations oflumber, e.g., 2×4 studs, or other common features, e.g. pipes,electrical conduit, etc. can be matched on a feature recognition basiswith the data as it is acquired. Such process may be used to (a) labelor color code a detected feature and (b) to optimize and sharpen imagesby adjusting the irregularly sampled density map to match the mostlikely distribution of actual hidden structures.

Rotation and alignment of measurements made by embodiments of thepresent invention may also be considered. In general, the accuracy ofposition knowledge is limited, as is the ability of the user tohand-hold an inspection apparatus in fixed orientation as it is movedover a surface. Relative motion sensing using inertial sensors, forexample, may drift and slippage may occur in embodiments employingrotational contact sensors. Embodiments of the present invention mayinclude means for maintaining consistency in the recorded data sets evenin the presence of such deficiencies. Rotation can in many embodimentsbe tracked by suitably supplementing accelerometer signals withknowledge of which way is down with respect to gravity. Knowledge ofdevice rotation and orientation may be used to compensate the sensorsampling functions relative to the orientation of data map 250. Devicerotation may also be considered in determining directions of relativemotion of the inspection apparatus. Errors in position determination andknowledge of device rotation may be used to compensate data in map 250for changing alignment and device orientation during repeatedmeasurements made at nearby points. For example, it is a natural humaninclination to move a hand-held inspection apparatus over a surface in away that tends to fill area sparsely as one might color in a region witha crayon. By monitoring the alignment of new data acquired in nearlyrepeated positions with previously acquired data in data map 250,embodiments of the present invention may detect device slippage,rotation and other spatial calibration anomalies. In simple embodiments,an alarm may warn the user that data acquisition is not synchronized, atwhich time data collection may be terminated. The inspection apparatusmay query the user as to whether to restart the scan. In moresophisticated embodiments, the acquired data may be re-oriented through,for example, an affine transform of the existing map to best fit (in anL¹ or L² sense) the new data, thereby accounting for device rotation andslippage. Other transforms, such as shrinking or expanding certainrecorded trajectory regions, may be used in conjunction with the presentinvention as well.

Other methods of feature tracking may be used in embodiments of thepresent invention to align a previously established data map to newdata. As used herein, a measurement field refers to a two-dimensionalsub-region of a data assemblage that is to be aligned with a similartwo-dimensional sub-region of another. Cross-correlation, for example,may be applied to align measurement fields of new and previouslyacquired data. Such alignment may be augmented by applying Gaussianblurs of the two measurement fields at various scales, or by otherrelated preprocessing methods. Alternatively, specific features such ascorners or edges may be located and mapped from one measurement field toanother, by which tie points may be established and an affine transformcalculated. Similarly, computationally generated features such as ScaleInvariant Feature Transform (SIFT) signatures may be computed and mappedfrom one to another.

In addition to allowing for incidental positional accuracy variations,certain embodiments of the present invention may also afford the userthe ability to discontinue, and then subsequently resume acquisition ofa data map 250. This will permit a user to, for example, begin scanning,say, a wall, to move the sensor subsystem 120 away from the surface forsome period of time, and then to return the sensor subsystem 120 to thesurface to resume the scan. By maintaining precise position information,such as a scan origin, resuming data collection to extend an existingdata map 250 can be achieved in a straightforward manner by suitabletechniques known in the art.

In the absence of precise position information, embodiments of thepresent invention can implement a process similar to the positionaldrift compensation discussed above. The inspection apparatus 100 mayacquire sufficient new data so that a new data map can be alignedrelative to the previously populated data map, and the informationcontained in each data map may be integrated into a single operatingdata map 250. This permits one additional mode of operation in certainembodiments of the invention, i.e., the integration of multiple separatedata maps. By using feature alignment techniques, such as SIFT, data forseveral regions of a wall may be acquired separately and then stitchedusing suitable merging and aligning techniques into a larger data map250 based on overlapping features.

FIG. 3 illustrates an exemplary process 300 by which the presentinvention may be embodied. Upon entry, exemplary process 300 transitionsto operation 305 by which map 250 is established. For example, thespatial arrangement and desired resolution, as well as the mappingfunction M(x, y) may be defined. Exemplary process 300 transitions tooperation 310, whereby a scan origin (i, j)=(0, 0) may be establishedrelative to which the position of sensor subsystem 120 may be tracked.The scan origin (0, 0) may be established, for example, at the positionat which initial contact of sensor subsystem 120 with surface 115 ismade, by operation of a user control, by a position of a knownstructural marker, or by means of a known positioning signal, such as isused in GPS, among others.

Exemplary process 300 transitions into a data acquisition loopcomprising operations 315-345. In operation 315, a characteristicmeasurement F_(k)(i, j) is obtained at the current position of sensorsubsystem 120 relative to the scan origin (0, 0). In operation 320, anaccumulated image corresponding to map 250 is updated to include datafrom the latest measurement F_(k)(i, j). The update operation 320 mayinclude re-computing values at (x, y) that correspond in position to thecontact area 255 corresponding to measurement F_(k)(i, j). In certainembodiments of the present invention, once the accumulated image hasbeen updated, the measurement F_(k)(i, j) is no longer required and maybe discarded. Process 300 may then transition to operation 325, wherebythe updated image is processed for presentation and displayed viagraphics subsystem 150.

In operation 330, it is determined whether the user has completed thescan, such as, for example, by removing sensing subsystem 120 fromsurface 115 or by activating a suitable user control. A scan, as usedherein, refers to a data acquisition cycle sufficient to cover aninspection region of interest. If the user has completed the scan,exemplary process 300 is terminated. However, if it is determined inoperation 330 that the user has yet to complete data acquisition andprocessing, exemplary process 300 transitions to operation 335, by whichit is determined whether sensor subsystem 120 has been moved. Operation335 may not be explicitly performed, since data sampling can occur evenregardless of whether sensing subsystem is moved. If operation 335evaluates as true, exemplary process 300 transitions to operation 340,whereby an updated position (i, j) of sensor subsystem 120 is obtained.Process 300 may then transition to operation 345, by which conditionsare evaluated as to whether measurement operation 315 is to be repeated.As is illustrated in FIG. 3, certain embodiments of the presentinvention implement a wait period 343, such as through a predeterminedprocessing delay, before another measurement operation 315 is performed.Waiting period 343 need not be explicit; it may be the delay inherent tocomplete operations 315-345 in each data acquisition and processingcycle. In other embodiments, waiting period 343 may be established tomaintain a fixed sample rate. Once the waiting period 343 has lapsed,exemplary process 300 transitions back to operation 315, whereby a newmeasurement F_(k)(i, j) is obtained and the data acquisition cycle315-345 is repeated.

In an alternative embodiment of the present invention, operation 345 isimplemented by operation 347, by which a determination is made as towhether motion threshold criteria MIN has been met. For example, ifsensor subsystem 120 has not been moved sufficiently far from itsprevious position, measurement data F_(k)(i, j) for that position isneither obtained, used to update previously accumulated data, nordisplayed. On the other hand, upon sensor subsystem 120 being moved to aposition that meets the threshold criteria of operation 347, exemplaryprocess 300 only then transitions to operation 315, whereby a new dataacquisition cycle 315-345 begins. Such motion thresholding may providebenefits by, for example, preventing slower processing hardware frombecoming overwhelmed with extra spatial samples. In certain embodiments,spatial sampling can be fixed to an approximate grid, such as map 250,via motion thresholding, thereby reducing some of the signal processingoverhead associated with non-uniform and irregular samples. When soembodied, threshold MIN sets the resolution Ry, Ry illustrated in FIG.2B. Moreover, motion thresholding may also be used stabilize the imageon the display 152 as the accumulated image displayed thereon iscontinuously updated, reducing jitter and making it easier for the userto interpret. Such means may also be employed only with respect to thedisplay updates, while still performing updates to the density estimatescontinuously. In certain embodiments of the invention, smoothing, suchas through a time-average, may be employed to filter display changes foreasier viewing.

It is to be understood that previously collected and processedmeasurement data may be displayed without further data collection. Incertain embodiments of the present invention, a previously processeddata map 250 may be displayed to correspond in position with thelocation at which the data were originally collected. That is, the datadisplayed in display 152 may be updated to reflect the hidden structureat the location of sensor subsystem 120, as determined from previousscanning operations.

Certain advantages and benefits of the present invention will now bedescribed with reference to a particular application, i.e., determiningand displaying structure hidden behind a wall, as is illustrated in FIG.4. For purposes of description and not limitation, it is to be assumedthat all of the subsystems described with reference to FIG. 1, i.e.,sensor subsystem 120, processing subsystem 140, graphics subsystem 150and communications subsystem 130, are contained within a single housingas inspection apparatus 440. An exemplary embodiment of such a systemconfiguration is illustrated in FIGS. 5A-5C as inspection apparatus 500.The inspection apparatus 500 includes a housing 510 to contain thesubsystems thereof. The housing 510 has disposed on an upper surfacethereof a display 515 and one or more user controls 520. Exemplary usercontrols 520 provide an interface for the user to control variousoperations of inspection apparatus 500. On the lower surface of housing510, there is disposed a position/motion sensor 540, a characteristicmeasurement sensor 530, and a marking device 550. The exemplaryposition/motion sensor 540 is a high-sample-rate optical sensorincluding a light source 542, such as an LED or semiconductor laser, anda receiver 544, such as a photo diode. Alternatively, as is illustratedin FIG. 5C, position/motion sensor may comprise a ball 570 mechanicallycoupled to orthogonal rotational encoders 572, 574. The underside ofhousing 510 may further include a plurality of low-friction inserts 512to facilitate movement of inspection apparatus 500 across the surface.

Returning now to FIG. 4, it is to be assumed that inspection apparatus440 is configured in a manner similar to inspection apparatus 500 andincludes a density sensor as the characteristic measurement sensor, ahigh-sample-rate optical motion detector as the position/motion sensorand a housing to contain sensor subsystem 120, processing subsystem 140,graphics subsystem 150 and communications subsystem 130. Inspectionapparatus 440 may be placed against wall surface 410 to obtainmeasurements of density at locations in inspection region 400. As isillustrated in FIG. 4, exemplary inspection region 400 includes two wallstuds 422, 428, a pipe 426, an electrical box 436, and electricalconduit sections 432, 434, all of which are obscured by wall surface410. Inspection apparatus 440 may be translated in multiple directionsover the wall surface 410, whereby signals indicative of hiddenstructure in the inspection region 400 are obtained. The density andposition signals may be processed by processor subsystem 140, such as byexemplary process 300 described above. As inspection apparatus 440 ismoved along a trajectory, which may be in one, two or three dimensions,density readings are taken and used to update the accumulated image map,as described with reference to FIG. 2B and FIG. 3, which may then bedisplayed on display device 442, as illustrated by two-dimensional image470. Areas in inspection region 400 not yet sampled may be indicated bya suitable fill pattern on display 442 (not illustrated), whereby theuser is informed where data collection has not been performed. Thus, theaccumulated image will appear to the user as being filled-in withincreasing completeness and detail as inspection apparatus 440 is movedalong the scan trajectory in overlapping sensed regions.

In certain embodiments of the present invention, an image may berendered in memory and such rendered image is referred to herein asmemory image 450. Memory image 450 comprises pixel values derived frommapped density measurements that have been made during an inspectionscan of inspection region 400. Additionally, memory image 450 may bederived from entries of a similar data structure containing higher orderdata. For example, memory image 450 may comprise integer valuesgenerated from respective floating point values stored elsewhere inmemory. When so embodied, memory image 450 is a reduction of the datamap 250 to a gridded set of pixel values, e.g., color code values,representative of the accumulated position-indexed values comprising thedata map 250. It is to be understood that while memory image 450 isillustrated in FIG. 4 as a complete image of inspection region 400, theactual number of assigned pixel will depend upon the progression of theinspection scan. In FIG. 4, changes in density are illustrated throughgrid spacing within representations of hidden objects, where finer gridspacing indicates a higher density than coarse grid spacing. It is to beunderstood that FIG. 4 is schematic and images 450, 470 are depictedusing black and white line art for illustration purposes. Certainembodiments of the present invention may employ a meaningful codingscheme, such as through grayscale or coded colors, to indicate detecteddensity ranges, specific material property types, etc.

In memory image 450, wall stud 422 is represented by pixels in theregion 452, wall stud 428 is represented by pixels in region 458, pipe426 is represented by pixels in region 456, junction box 436 isrepresented by pixels in region 466, conduit 432 is represented bypixels in region 462 and conduit 424 is represented by pixels in region454. It is to be noted that a change in density may be observed inregion 464 that corresponds to a borehole 434 in wall stud 422 toaccommodate conduit 432. Moreover, it is to be observed that a higherdensity region 468 represents a location in inspection region 400 wherepipe 426 is closest to the backside of wall 410.

Image 470 displayed on display device 442 may be only a portion ofmemory image 450. In certain embodiments of the present invention, image470 in display device 442 acts like a virtual window that is alwayscentered at the location of the inspection apparatus 440. As inspectionapparatus is moved from one location to another, as illustrated by thelocation of inspection apparatus 440′, display device 442′ and image470′, the depiction of the structure behind wall 410 may appear toscroll, left-right and up-down, with the motion of inspection apparatus400. This may be achieved in a number of ways, such as by representingthe display area as a matrix S of pixel values spaced at fixedintervals, where each pixel value is assigned a value S(m, n), where mand n are the coordinates in the display 442 of the corresponding pixel.The window origin (0, 0)_(w), which is not to be confused with thespatial origin (0, 0) where the scan originated, may be assigned to thecenter of the display 442. The current location of inspection apparatus440 relative to the established spatial origin (0, 0) at any given timemay be given by (i_(now), j_(now)), and processing subsystem 140 mayupdate the image 470 in display 442 by retrieving corresponding pixelvalues from memory image 450:

for each (x_(k), y_(k)) in memory image 450 D;set S(x _(k) −i _(now) ,y _(k) −j _(now))=D(x _(k) ,y _(k));

increment k and continue until image 470 is complete.

In certain embodiments of the present invention, the user maydynamically zoom in and out on image 470. This may be accomplished bysuitable rescaling techniques whereby the user can visualize the overallhidden structure while zoomed-out and locate details while zoomed-in.Certain embodiments of the present invention may provide apicture-in-picture display, showing the overall structure at zoomed-outscale overlaid with a zoomed-in detail image.

The dynamic range of display 442 may also be scaled, both automaticallyand by user control. In certain embodiments of the present invention,the dynamic range data in memory from which memory image 450 isconstructed, which may be implemented by, for example, floating pointvalues, will be much greater than that of display 442, which may beconfined to only integer values. Thus, inspection apparatus 440 maystore a broad range of densities, which may scaled for purposes ofdisplay. By storing floating point numbers, for example, the displayrange can be adjusted to suit the range of the data. Other suitabletechniques for compressing the dynamic range of data for display mayalso be used in conjunction with the present invention without deviatingfrom the spirit and intended scope thereof. Storage of measurement datato achieve a broad dynamic range for purposes of display beneficiallyavoids local self-calibration requirements of the prevailing art, andthus can be used to acquire and monitor data continuously over a largespatial surface without reset.

Display 442 may also be adjusted by the user in brightness, contrast, orin other aspects so that features of interest are clearly visibletherein. For example, a user interested in finding wires or deeper tubesor pipes may adjust the contrast in display 442 so that finer detail ofsuch structure is displayed, while gross structure, such as wall studs,is set to a maximum value, or “clipped.” In certain embodiments, theuser may also select a logarithmic color scale or other rangingtechniques to accommodate simultaneous presentation of widely varyingstructure information.

FIG. 6A illustrates an exemplary system configuration suitable topractice the present invention. Exemplary data processing apparatus 600of FIG. 6A includes a processor 610 to, among other things, executeprocessing instructions that implement various functional modules, suchas those described below with reference to FIG. 6B. It is to beunderstood that the present invention is not limited to a particularhardware configuration or instruction set architecture of the processor610, which may be configured by numerous structures that performequivalently to those illustrated and described herein. Moreover, it isto be understood that while the processor 610 is illustrated as a singlecomponent, certain embodiments of the invention may include distributedprocessing implementations through multiple processing elements. Thepresent invention is intended to embrace all such alternativeimplementations, and others that will be apparent to the skilled artisanupon review of this disclosure.

The exemplary data processing apparatus 600 includes an input/output(I/O) system 617, through which the data processing apparatus 600 maycommunicate with peripheral devices and/or with external network devices(not illustrated), such as to remotely program the data processingapparatus 600, to upload and download preferred setting information, andto download acquired data maps, architectural plan files and the like.

Data processing apparatus 600 may include controls 615 by which dataprocessing apparatus 600 may be operated and controlled. Such controlsmay include buttons, keyboards, touch screens and/or other devicessuitable to provide input to the data processing apparatus 600. Astorage unit 646 may be utilized to store data and processinginstructions on behalf of the exemplary data processing apparatus 600and, as such, may include multiple segments, such as a code memory 642to maintain processor instructions to be executed by the processor 610,and data memory 644 to store data on which processor 610 performs datamanipulation operations. Storage unit 646 may include memory that isdistributed across components, to include, among others, cache memoryand pipeline memory. Data processing apparatus 600 may further include apersistent storage system 630 to store data and processing instructionsacross processing sessions. The persistent storage system 630 may beimplemented in a persistent memory device, such as a hard disk drive orflash memory.

Exemplary data processing apparatus 600 includes an inspection sensorsystem 635 comprising one or more characteristic measurement sensors anda position/motion sensor system 637 comprising one or more motiondetecting and/or position detecting sensors. Inspection sensor system635 and position/motion sensor system 637 may include suitable circuitryto condition analog signals and convert the analog signals to numericalvalues that can be machine-processed, such as by processor 610.

Data processing apparatus 600 may include a marking device 633, whichimplements processor-controlled marking of the surface of the inspectionregion, as is described more fully with reference to FIG. 8. Markingdevice 633 may be implemented in suitable hardware, such as inkjet, filmtransfer, thermal marking, stylus marking, etc., by which a surface canbe marked as the inspection apparatus is moved thereon. It is to beunderstood that such marking device 633 is optional and that a markingdevice that is not under processor control may also be utilized with thepresent invention without deviating from the spirit and intended scopethereof.

Exemplary data processing apparatus 600 includes a graphics subsystem640 to render and display images of hidden structure in accordance withthe present invention. Graphics subsystem 640 may include a dedicatedprocessor 643, and dedicated memory 645 in which memory images may berendered. Exemplary graphics subsystem 640 includes a display device 641to display images and other data to the user. Additionally, dataprocessing apparatus 600 may include a projecting device, such as amodulated laser, a liquid crystal display (LCD) projector, etc., bywhich an image of the hidden structure may be projected onto a surfaceof the corresponding inspection region. Projector implementations of thepresent invention are described with reference to FIGS. 10-11.

FIG. 6B illustrates an exemplary configuration of functional componentssuitable to practice certain embodiments of the present invention. Theexemplary system illustrated in FIG. 6B may be implemented throughprocessing instructions executed on the processor 620, and incooperation with other components as illustrated in FIG. 6A, form anexemplary inspection system 650 on the exemplary data processingapparatus 600. Alternatively, inspection system 650 may be implementedentirely in suitable hardware, such as through programmable logic,Application Specific Integrated Circuits (ASIC), and the like.

Inspection system 650 may include a process controller 660 to coordinateand control the interoperations of the functional components thereof perthe requirements of the implementation of the inspection system 650.Upon review of this disclosure, the ordinarily skilled artisan willrecognize a wide range of well-known process control methods andapparatuses by which a process controller 660 suitable for use with thepresent invention may be implemented. The present invention is intendedto encompass all such alternatives of the process controller 660,including multi-threaded and distributed process control methodologies.

Inspection system 650 may include a user interface 680 through which theinspection system 650 interacts with a user. The user interface 680 maybe implemented by a combination of hardware devices and suitablyprogrammed processing instructions executed by the processor 610 and/orby a dedicated processor 643 of graphics system 640. The user interface680 may be used to present hidden structure data to the user in ameaningful form on a display interface 682, such as described above, aswell as suitable data management interfaces, such as for hierarchicalfile storage, control functions, and other information recognized by theuser. The user interface 680 may interpret user manipulations of usercontrols 684, which may be implemented in a combination of hardware andsoftware, into messages and instructions that can be recognized by theprocess controller 660 to afford the user interactivity with and controlover the inspection system 650. The user controls 684 may includecontrols 615 described above, and may also include software implementedcontrols on the display interface 682, such as toolbars and/or buttons,menus of commands, text command entry blocks, and other suitablesoftware controls. The foregoing description of the user interface 680may be met by a suitably configured graphical user interface (GUI), theimplementation details of such will be omitted in the interest ofconciseness.

Inspection system 650 may include a storage area 679 in which data canbe temporarily stored and retrieved as required during various dataprocessing operations. Such storage area may be implemented in the datamemory segment 644 of storage unit 646. Additionally, inspectionapparatus 650 may include a database 675 to store, among other things,libraries and templates of auxiliary data to assist the user indetermining the nature of the hidden structure. For example, survey orblueprint plan information may be stored in database 675 by which a usermay compare actual structure, as obtained by the inspection system 650,to expected structure contained in an engineering plan file. Datacontained in an engineering plan file may be overlaid onto accumulatedimage data to assist in the comparison. Accordingly, database 675 may becoupled to a larger database through a communication network andpertinent engineering files may be downloaded from an external databaseinto database 675 as needed.

Inspection system 650 may include an inspection processing unit 677 toprocess sensor data from inspection sensor system 635 andposition/motion system 637. For example, inspection processing unit 677may associate position data from position/motion sensor 637 tocharacteristic measurement data from inspection sensor 635.Additionally, inspection processing unit 677 may establish a scanningorigin, compute position data relative to the scanning origin and maycompensate position data for any sensor offset between a position sensorof position/motion sensor system 637 and one or more correspondinginspection sensors in inspection sensor system 635. Inspectionprocessing unit 677 may store the associated characteristic measurementdata and position data in storage area 679 for use by other functionalunits. Inspection processing unit 677 may also revise position data tocompensate for drift in the position of inspection system 650. Forexample, the accumulated image may be shifted, stretched, rotated, etc.,to maintain the position of the image in the display when substantiallyequivalent, but slightly different measurement locations (i, j) arevisited more than once in a scan.

Data processing unit 667 may retrieve measurement data from storage area679 and map such measurement data into a data structure, such as therectangular memory grid described with reference to FIG. 2B.Additionally, as new measurement data are obtained during scanningoperations, data processing unit 667 may update the mapped datastructure by adding new data points where initial measurement data areobtained and by re-computing values for data points for whichmeasurement data has been previously obtained. Upon completing the datamapping and other data processing operations that are based oncharacteristic measurements, data processing unit 667 may evaluatewhether measurement data are to be discarded, thereby releasingresources for newly obtained data.

Exemplary inspection system 650 includes a graphics processing unit 663to prepare the data in the previously-described mapped data structurefor display. For example, graphics processing unit 663 may convertfloating point numbers in the mapped data structure to integer valuescorresponding to colors, shading, fill patterns, etc., and to render amemory image using the integer values. Graphics processing system 663may further relatively scale the mapped data to highlight certainstructural features, may implement contrast and brightness processing,zooming, window scrolling, data centering, graphical overlay and othersuch graphical operations per the application requirements of thepresent invention. The present invention is not limited to anyparticular set of graphical operations and the ordinarily skilledartisan will recognize numerous image processing and display techniquesthat can be used in conjunction with the present invention withoutdeparting from the spirit and overall scope thereof. Additionally,graphics processing unit 663 may generate image data to be presented ina virtual window, such as described above.

Exemplary projection processing unit 673 provides additional graphicalsupport for projecting an image of hidden structure onto a surface. Incertain embodiments of the present invention, projection processing unit673 may provide alignment and registration processing, by which an imageof structure in a large inspection region may be projected onto theobscuring surface in proper alignment. For example, a mark may beapplied to the surface at the scan origin, such as by a marking devicedescribed below, and projection processing unit 673 may insert oroverlay a corresponding mark in the image to be displayed. Accordingly,a user may align the mark on the surface and the corresponding mark inthe projected image, thus displaying the structure represented in theimage on the surface in the inspection region at the at the actualphysical location of such structure. Additionally, projection processingunit 673 may format a data stream corresponding to a graphical depictionof the structure so that a suitable light modulator, e.g., a lasermodulator, an LCD projector modulator, etc., can project such graphicaldepiction of the structure on a surface.

Marker processing unit 685 formats marking data, which are transferredto a surface being scanned through marking device 633. Marker processingunit 685 may generate marking patterns representative of hiddenstructure and provide such patterns to marking device 633.Accelerometers and/or other devices may be used to track scanning speedand, in conjunction with the position data produced by inspectionprocessing unit 677, the mark application timing of marking device 633can be controlled to overlay the markings on the target structure.

Certain embodiments of the present invention may include multipleinspection sensors to ascertain characteristics associated with hiddenstructure. Sensing modalities can be selected with deeper or withadjustable penetration depths so as to inspect deeper structure or tosense objects or occupants on the other side of an obstructing barrier.When multiple characteristic measurement sensor types are employed in asingle inspection apparatus, each sensor may be read while theinspection apparatus is positioned at a location (i, j), and thecharacteristic measurement values from each sensor may be associatedwith position data that has been compensated for spacing betweensensors. In certain embodiments of the present invention, informationfrom multiple diverse sensors may be combined to present additional,useful information to a user. For example, a metal detecting sensor inproximity to, say, a material density sensor can be used tosimultaneously accumulate both density and material information. Thus,processor subsystem 140 may produce an image in which metal objects inone color coding scheme may be overlaid in a similar or distinct codingwith density data. Other embodiments of the present invention mayincorporate both absolute density and edge detection sensors to displaygeneral density patterns with overlaid crisp edge indications of, say,studs and other sharply delineated objects. Certain embodiments of thepresent invention may incorporate electrical activity sensors to provideindications of A/C or D/C currents behind an obscuring barrier todistinguish, for example, house wiring from, say, flexible tubingcarrying water.

In FIG. 7A, there is illustrated an exemplary sensing system 700comprising an array 720 of sensors 725 by which data acquisition may beachieved. The array 720 may be disposed on a suitable substrate 710, andeach individual sensing element 725 generates a signal indicative of acharacteristic measurement that is mapped or otherwise factored into aninformational image. Such arrays may afford data acquisition over abroader surface area in an inspection region with each pass of theinspection apparatus. The individual sensor elements 725 may produce thesame or different information about the target structure withoutdeparting from the spirit and intended scope of the present invention.When different characteristic information is available, such may becombined to indicate a single structural aspect, such as object class(metal pipe vs. plastic pipe, for example), or may be overlaid one onanother to indicate separate structural aspects.

FIG. 7B illustrates an alternative sensing system 750 in which twosensing elements 763, 767 are disposed on a substrate 760. When soembodied, sensor 763 may operate preferentially in the left-right edgeorientation due to its greater contact area in that direction, whilesensor 767 may operate preferentially in the up-down edge orientation.Because the sensing occurs in separate physical locations, measurementinterference between sensor data may be minimized. However, because thespatial sensing is achieved by moving the inspection apparatus over awall or other target surface in multiple directions, both sensingelements 763, 767 may be used to sample substantially the same spatialpoints in an inspection region and the acquired information may beutilized in an accumulated image update, such as that described withreference to FIG. 2B.

Any number of additional sensors may be included in an arrangement likethat illustrated in FIG. 7B, including arrangements of different sensortypes. For example, certain embodiments of the present invention mayincorporate two orthogonally-oriented edge sensors and a third metaldetector element, all of which would sense locally and substantiallyindependently of their neighbors, while the combined information isrecorded and spatially integrated by processing subsystem 140.

Referring now to FIG. 8, there is illustrated an inspection apparatus800 similar to that of FIG. 5. As described with reference to FIG. 5,inspection apparatus 800 includes a marking device 805 disposed on theunderside of the housing to mark surface 850 with, for example, inkpatterns 833, 837 indicative of the location of hidden items ofinterest. Marking device 805 may be disposed on inspection apparatus 800to mark a region identified by indicator 810 in display 840, such thatthe indicated region, such as the edge of object 815, 817 is marked asthe user moves inspection apparatus 800. Additionally, the markingpatterns applied by marking device 805 may indicate density or otherproperties by altering the nature of the applied markings. For example,marking pattern 833, corresponding to displayed region 815, may indicatea denser object or region, whereas marking pattern 837, corresponding todisplayed region 817, may indicate a relatively less dense object orregion. It is to be understood that while marking device 805 isillustrated in axial alignment with the inspection apparatus 800,marking device 805 may be located elsewhere without departing from thespirit and intended scope of the present invention.

Marking device 805 may be activated manually or automatically. Forexample, in one embodiment of the present invention, marking device 805applies ink only when the user enables a marking mode, such as by a usercontrol 820. Alternatively, marker device 805 may be a simple mechanicaldevice, such as a pen or scribe pushed into place by the user to recordplaces of interest on the wall.

In certain embodiments of the present invention, such as is illustratedin FIG. 9A, inspection apparatus 900 is divided into a sensing head 910,which is moved over a surface 950, and a processing and display unit930. The sensing head 910 may be communicatively coupled to processingand display unit 930 by a suitable communications link 920, which may bea wireless link, such as a WiFi or Bluetooth link, or a wired link, suchas a Universal Serial Bus (USB) connection. When so embodied, a largerdisplay may be incorporated into the inspection apparatus 900, which maybe held separately or placed on a stand at a fixed location. In certainembodiments of the present invention, processing and display unit 930 isimplemented on general purpose computing machinery, such as, forexample, on a laptop, tablet, netbook, or palm-top computer, executingprocessing software to receive signals from the sensing head 910 overcommunication link 920 and to accumulate and display acquiredinformation.

Due to the flexibility in distributing functionality across separableunits, the present invention may be embodied in a variety of uniquesystem configurations. For example, the exemplary inspection apparatus950 illustrated in FIGS. 9B-9C utilizes a standard computer mouse 915communicatively coupled to processing and display unit 960 through acommunication link 922. The processing and display unit 960 includes adisplay 968 disposed on the separable housing 962, user controls 964 andone or more characteristic measurement sensors 970. The inspectionapparatus 950 may utilize the position/motion sensor 975 on mouse 915 todetermine location and such location is communicated in a standard wayto processing and display unit 960. For example, a mouse 915 mayimplement a wireless transmitter (not illustrated) to communicateposition information to a remote device, typically a computer, over awireless communication link 922. Processing and display unit 960 mayinclude a wireless receiver (not illustrated) to intercept the locationsignal from mouse 915 and may utilize position data therein in a mannersimilar to that already described above.

In certain embodiments of the present invention, as is illustrated inFIG. 10, a handheld inspection apparatus 1000 includes an opticalprojection device 1010, such as a diode laser (not illustrated), whichprojects a spatially modulated beam onto the inspected surface togenerate an image 1020 of the hidden structure directly on the targetsurface. In certain embodiments of the present invention, image 1020includes detailed information, such as density illustrated in projectedregion 1023. In other embodiments, projected image 1020 includes simpleinformation, such as edges illustrated in region 1027. The projectedimage 1020 may be generated to reflect the hidden structure at theposition of the inspection apparatus 1000 and such image may be updatedin a manner similar to that described above with reference to FIG. 2B asthe position of inspection apparatus 1000 changes. Thus, image 1020 maybe generated to appear as though fixed in space on the inspected surfacewith each component of the hidden structure projected in proper positionand scale.

The means for projection of the image may, in other embodiments, bephysically separated from the sensing device, such as is illustrated inFIG. 11. A processing and display unit 1110 may receive information froma sensing head 1130 over a communication link 1120 and may include aprojector 1115 to project structural information directly on the surfaceof the wall 1150 in accurate locations and scale to reflect the hiddenstructure. In certain embodiments of the present invention, projector1115 projects not only location data, but characterization data as well.For example, projector 1115 may be an LCD or microelectromechanicalsystem (MEMS) minor projector. By projecting position-accurate hiddenstructure information over a broad area, multiple users can availthemselves of information for inspection, marking, or other purposes.

The descriptions above are intended to illustrate possibleimplementations of the present inventive concept and are notrestrictive. Many variations, modifications and alternatives will becomeapparent to the skilled artisan upon review of this disclosure. Forexample, components equivalent to those shown and described may besubstituted therefore, elements and methods individually described maybe combined, and elements described as discrete may be distributedacross many components. The scope of the invention should therefore bedetermined not with reference to the description above, but withreference to the appended claims, along with their full range ofequivalents.

What is claimed is:
 1. An apparatus to inspect a region of interest forphysical structure through a surface therein, the apparatus comprising:at least one sensor configured to generate a characteristic signal asthe sensor is moved across the surface in the region of interest, thesensor defining a contact area on the surface over which at least onephysical characteristic at each measurement location on the surface towhich the sensor is moved is characterized by an attribute of thecharacteristic signal; a memory comprising storage locationslogically-arranged in accordance with a coordinate system to representmap locations of a data map; a processor configured to: determine themap locations representing the contact area in the coordinate system ofthe data map for each measurement location; estimate values of astructural characteristic of the physical structure from the quantifiedattribute of the characteristic signal for the map locationsrepresenting the contact area at the measurement location at which thecharacteristic signal was generated; and store the computed values atthe respective map locations of the data map; and a display to generatea two-dimensional visual image from the data map.
 2. A method ofcharacterizing physical structure through a surface in a region ofinterest, the method comprising: establishing a data map in a memoryhaving map locations logically arranged in accordance with apredetermined coordinate system; generating a characteristic signal byat least one sensor as the sensor is moved over the surface, thecharacteristic signal having an attribute quantifying a physicalcharacteristic over a contact area defined by the sensor on the surfaceat each measurement location at which the sensor is moved; determining,by a processor, the map locations representing the contact area in thecoordinate system of the data map for each measurement location;estimating, by the processor, values of a structural characteristic ofthe physical structure from the quantified attribute of thecharacteristic signal for the map locations representing the contactarea in the data map for the measurement location at which thecharacteristic signal was generated; storing the estimated values of thestructural characteristic at the respective map locations of the datamap; and displaying, on a display, a two-dimensional image of pixelsarranged per the predetermined coordinate system and assigned pixelvalues corresponding to the estimated structural characteristic valuesin the data map.
 3. The method of claim 2, wherein estimating the valuesof the structural characteristic comprises: computing, by the processor,the values of the structural characteristic for each of the maplocations in accordance with a sampling function defined over thecontact area; and updating, by the processor with the computed values ofthe structural characteristic, the estimated values of the structuralcharacteristic stored at memory locations corresponding to the contactarea at other measurement locations at which the sensor was previouslymoved.
 4. The method of claim 3, wherein computing the values of thestructural characteristic comprises: weighting, by the processor inaccordance with the sampling function, the attribute of thecharacteristic signal generated at the measurement location across thememory locations representing the contact area in the data map.
 5. Themethod of claim 4, wherein updating the estimated values comprises:convolving, by the processor, the weighted characteristic signal in thememory locations representing the contact area with the estimated valuesof the structural characteristic stored at the memory locationscorresponding to the contact area at the other measurement locations. 6.The method of claim 2, wherein the estimated structural characteristicis density.
 7. The method of claim 2, further comprising: generating apositioning signal by the at least one sensor; and determining, by theprocessor, the measurement location relative to the other measurementlocations from the positioning signal.
 8. The method of claim 2, furthercomprising: moving the at least one sensor, the memory and the displayon a free-form trajectory in a common housing held in one hand of auser.
 9. The apparatus of claim 1, wherein the processor is furtherconfigured to: compute the values of the structural characteristic foreach of the map locations in accordance with a sampling function definedover the contact area; and update, with the computed values of thestructural characteristic, the estimated values of the structuralcharacteristic stored at the memory locations corresponding to thecontact area at other measurement locations at which the sensor waspreviously moved.
 10. The apparatus of claim 9, wherein the processor isfurther configured to: weight, in accordance with the sampling function,the attribute of the characteristic signal generated at the measurementlocation across the memory locations representing the contact area inthe data map.
 11. The apparatus of claim 10, wherein the processor isfurther configured to: convolve the weighted characteristic signal inthe memory locations representing the contact area with the estimatedvalues of the structural characteristic stored at the memory locationscorresponding to the contact area at the other measurement locations.12. The apparatus of claim 1, wherein the at least one sensor comprises:an inspection sensor configured to generate the characteristic signal;and a positioning sensor configured to generate a positioning signal bywhich the measurement location is determined relative to othermeasurement locations as the positioning sensor is moved across thesurface.
 13. The apparatus of claim 12, wherein the positioning sensoris includes encoders that generate the positioning signal as relativedisplacement in a Cartesian coordinate system.
 14. The apparatus ofclaim 1, wherein further comprising: a housing in which the inspectionsensor, the positioning sensor, the processor and the display arecommonly housed.
 15. An apparatus to inspect a region of interest forphysical structure through a surface therein, the apparatus comprising:a position sensor configured to generate a positioning signal by which ameasurement location is determined relative to other measurementlocations in a predetermined coordinate system; an inspection sensorconfigured to generate a characteristic signal at each measurementlocation on the surface to which the sensor is moved, the characteristicsignal quantifying a physical characteristic of the physical structureby an attribute thereof; a memory comprising storage locationslogically-arranged in accordance with the coordinate system to representmap locations of a data map; a processor configured to store values of astructural characteristic of the physical structure estimated from thequantified attribute of the characteristic signal for the map locationsrepresenting the measurement location determined from the positioningsignal.
 16. The apparatus of claim 15, further comprising a displayconfigured to generate a two-dimensional visual image from the data map.17. The apparatus of claim 15, wherein the inspection sensor defines acontact area on the surface at the measurement location over which thephysical characteristic is quantified by the attribute of characteristicsignal.
 18. The apparatus of claim 17, wherein the processor is furtherconfigured to: determine the map locations representing the contact areain the coordinate system for each measurement location; compute thevalues of the structural characteristic for each of the map locations inaccordance with a sampling function defined over the contact area; andupdate, with the computed values of the structural characteristic, theestimated values of the structural characteristic stored at the memorylocations corresponding to the contact area at other measurementlocations at which the inspection sensor was previously moved.
 19. Theapparatus of claim 18, wherein the processor is further configured to:weight, in accordance with the sampling function, the attribute of thecharacteristic signal generated at the measurement location across thememory locations representing the contact area in the data map.
 20. Theapparatus of claim 19, wherein the processor is further configured to:convolve the weighted characteristic signal in the memory locationsrepresenting the contact area with the estimated values of thestructural characteristic stored at the memory locations correspondingto the contact area at the other measurement locations.
 21. Theapparatus of claim 15, further comprising: a housing in which theinspection sensor, the positioning sensor and the processor are commonlyhoused.
 22. The apparatus of claim 15, wherein the housing is movableacross the surface in one hand of a user.